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CVE-2026-55144 is a vulnerability in Microsoft’s Cryptography API: Next Generation (CNG), the modern cryptographic subsystem introduced in Windows Vista and used extensively in Windows 11 and Windows Server for encryption, hashing, digital signatures, and certificate validation. The flaw is classified under CWE-325 – Missing Cryptographic Step, meaning that a required cryptographic operation—such as a verification, hash extension, or integrity check—was simply omitted from a critical code path within CNG. This omission creates a security boundary bypass where data that should have been cryptographically protected can be altered without detection.
An authorized attacker with local access and low privileges can exploit this missing step to tamper with cryptographic material or protected data. The attack does not require user interaction, has low attack complexity, and can be executed entirely from within an already compromised session or through a malicious low‑privileged service. Because the missing step is part of CNG’s internal processing, the tampering occurs at the API level—the attacker does not need to break encryption or forge keys; they merely need to reach the vulnerable code path and supply crafted inputs that skip the missing verification.
The vulnerability is scored with CVSS 3.1 base score 7.1 (High) with vector AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N. This indicates a local attack vector, low complexity, low privileges required, no user interaction, and high impacts on both confidentiality and integrity, with no impact on availability. Microsoft’s own security advisory confirms that exploitation is “less likely” and no public proof‑of‑concept or in‑the‑wild exploitation has been observed, but the potential for data exposure and integrity violation is significant, especially on shared servers, developer workstations, and virtual desktop infrastructures where multiple tenants or service accounts coexist.
Affected products include Windows 11 versions 24H2, 25H2, and 26H1, as well as Windows Server 2022 and Windows Server 2025 (including Server Core installations). The vulnerability was patched on July 14, 2026, through the monthly cumulative updates: KB5101650 for Windows 11 24H2/25H2, and KB5099540 for Windows Server 2022. Systems that have not applied these updates remain vulnerable to local data tampering. Administrators are advised to prioritize patching on systems that handle sensitive cryptographic material, such as certificate authorities, domain controllers, and systems using CNG for secure storage or communication.
DailyCVE Form:
Platform: ……. Windows CNG
Version: …….. 11/Server 2022+
Vulnerability :.. Missing crypto step
Severity: ……. High (7.1)
date: ………. 2026-07-14
Prediction: ….. Patched July 2026
What Undercode Say
Analytics & Detection Commands
Check your Windows build number to verify if the patch is installed:
Get the current OS build Or via wmic wmic os get buildnumber
For Windows 11 24H2, the patched build is 26100.8875 or higher. For 25H2, it is 26200.8875 or higher. For 26H1, it is 28000.2525 or higher. For Server 2022, the patched build is 20348.5386 or higher. For Server 2025, it is 26100.33158 or higher.
Check installed updates for KB5101650 or KB5099540
Get-HotFix | Where-Object { $_.HotFixID -match "KB5101650|KB5099540" }
If the update is missing, the system is vulnerable. You can also query the registry to see if the update is applied:
Get-ItemProperty -Path "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion" | Select-Object BuildLabEx
Monitoring for Suspicious CryptoAPI Calls
Use Sysmon or Windows Event Logs to monitor for unusual CNG operations. Event ID 1 (process creation) with command lines invoking certutil, makecert, or custom .NET applications using `System.Security.Cryptography` may indicate tampering attempts.
Enable detailed CNG logging (requires admin) wevtutil set-log "Microsoft-Windows-Crypto-NCrypt/Operational" /enabled:true /retention:false /maxsize:1073741824 Query recent CNG events Get-WinEvent -LogName "Microsoft-Windows-Crypto-NCrypt/Operational" -MaxEvents 20 | Format-List
Exploit
As of the latest advisory, no public exploit code has been released for CVE‑2026‑55144. Microsoft reports that exploitation is “less likely” and no in‑the‑wild attacks have been detected. However, the vulnerability is locally reachable by any authenticated user with low privileges. The missing cryptographic step means an attacker could:
– Tamper with encrypted data – modify ciphertext or protected blobs without triggering integrity errors.
– Bypass signature verification – alter signed content and have it accepted as valid if the missing step is part of the verification process.
– Corrupt certificate chains – spoof the validity of ECC‑based certificates if the missing step affects elliptic curve operations.
The attack requires the attacker to already have local access (e.g., via a compromised user account, malicious insider, or a low‑privileged service). Once inside, they can call the vulnerable CNG functions with specially crafted parameters to skip the omitted cryptographic check. No privilege escalation is directly provided; the impact is limited to data the attacker can already access, but that data’s confidentiality and integrity are at risk.
Protection
The only complete protection is to install the July 2026 cumulative security update:
– Windows 11 24H2 / 25H2: Install KB5101650 (build 26100.8875 / 26200.8875).
– Windows 11 26H1: Install the corresponding cumulative update (build 28000.2525).
– Windows Server 2022: Install KB5099540 (build 20348.5386).
– Windows Server 2025: Install the July 2026 cumulative update (build 26100.33158).
These updates are available via Windows Update, WSUS, or the Microsoft Update Catalog.
Additional mitigations (if patching is delayed):
- Restrict local logon and service accounts to only those that absolutely need them.
- Use Application Control (WDAC) or AppLocker to prevent untrusted executables from running.
- Monitor for unusual CNG API calls using Sysmon or EDR solutions.
- Consider temporarily disabling CNG features that are not essential, though this may break functionality.
Impact
Successful exploitation of CVE‑2026‑55144 leads to:
- Loss of Confidentiality – an attacker can read protected data that should have been encrypted or shielded by the missing cryptographic step.
- Loss of Integrity – an attacker can modify data in transit or at rest without detection, potentially leading to tampered configuration files, altered security policies, or corrupted authentication tokens.
- No direct Availability impact – the system remains operational, but the trustworthiness of cryptographic operations is undermined.
On shared environments (e.g., multi‑tenant servers, virtual desktop infrastructure, developer machines), this vulnerability is particularly dangerous because a low‑privileged user or compromised process can affect data belonging to other tenants or system services. While not a remote code execution flaw, it serves as a powerful post‑exploitation tool for attackers who have already gained a foothold, allowing them to manipulate sensitive cryptographic material and potentially pivot to higher‑value targets.
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Sources:
Reported By: nvd.nist.gov
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